This invention relates to a device for separating droplets of liquid from gases, in particular an oil separator for air. Separators for removing liquid droplets from gases are used, for example, for separating water and/or oil from air. Separators of this type are used in particular for removing oil from air in compressors.
Liquid droplets may accumulate in a stream of gas as it comes in contact with liquids. The liquid droplets may be entrained mechanically, e.g., as the gas flows through the liquid or when the stream of gas is passed over a liquid. In screw compressors, for example, air comes in contact with oil. The oil is used for sealing, cooling and lubricating the compressor. Liquid droplets may also be formed in a gas stream by condensation, e.g., liquid droplets are formed by condensation in a stream of vapor. Temperatures of approximately 200° C. may occur in the production of compressed air. Due to these temperatures, a portion of the oil that is supplied in the case of a screw compressor, for example, may evaporate. The oil vapor then condenses to form droplets and mist in subsequent cooling. The oil droplets of a screw compressor have a diameter on the order of approximately 0.01 μm to 100 μm.
Droplet separators are used for separating liquid droplets from gases. Droplet separators are capable of separating a liquid phase from a gaseous phase. Droplet separators may be used for cleaning exhaust air streams. With droplet separators, entrained liquid droplets can be separated from process gas flows. Corrosion or erosion of installation parts or caking or deposits on installation parts may be reduced by such separation. By reusing separated media the consumption of operating media can be reduced. Droplet separators are used, for example, for removing oil from compressed air.
Droplet separators may be constructed as inertial separators. In inertial separators, the inertia of the droplets is utilized to separate the droplets on walls. Inertial separators are suitable especially for larger droplets, usually with a droplet diameter of more than approximately 20 μm. A baffle plate is a simple form of droplet separator. With a baffle plate, a gas stream loaded with liquid droplets is directed at a plate, so that the gas stream undergoes a change in direction. Due to inertia, the droplets contained in the gas stream retain their direction, strike the plate and are diverted there. Another type of inertial separation makes use of centrifugal forces. In centrifugal separators, the gas stream is guided along a curved path. Due to the centrifugal forces, the droplets are guided on an outer path having the largest possible radius of curvature. Therefore, the droplets are concentrated in this outer area. The droplets may then be deposited on a wall along the outer area of the gas flow, for example. The droplets can then be diverted from the wall. Alternatively, it is also possible to remove only gas from the interior area of the gas stream having a low droplet concentration. Various types of cyclones, for example, may be used as centrifugal separators.
Droplet separators may be designed as a drainage element. With a drainage element, a gas stream loaded with liquid droplets is passed through a mesh-like and/or porous drainage structure. For example, a woven wire mesh or a nonwoven fleece, e.g., made of synthetic resin or glass fibers, may be used as the drainage structure. Droplets pass through the drainage structure more slowly than does the gas stream. Due to gravity, the droplets move toward the geodetically lower region of the drainage structure, collect there and can be removed.
The larger the droplets entrained in the gas stream are, the more efficient inertial separation is. Coalescing elements are used to increase droplet size. In coalescing elements the gas stream is passed through a mesh and/or porous coalescing structure. A woven wire mesh or a nonwoven fleece, e.g., made of plastic or glass fibers, may be used as the coalescing structure. The gas stream follows the flow lines. The droplets cannot follow the flow lines and remain adhering to the boundary surfaces of the coalescing structure. A liquid film forms on the coalescing structure. Small droplets combine to form larger droplets, i.e., they coalesce. The enlarged droplets leave the coalescing structure. Coalescing elements may also have a drainage effect. The droplets form the liquid film on the coalescing structure, move toward the geodetically lower region and can be drained out there. Therefore, a combined coalescing and drainage element may be designed. The larger droplets, which are therefore heavier, leaving the coalescing structure, fall in the gas stream and can also be removed from the gas stream in this way.
Depending on the field of use, persons skilled in the art will be aware of various combinations of drainage and coalescing elements as well as inertial separators for separating liquids from gases. The system described below is known for removing oil from compressed air from compressors. In a pressure vessel, a cylindrical flow baffle is introduced at the upper end. The cylinder formed by the flow baffle is open at the bottom toward the interior of the pressure vessel. The compressed air enters tangentially between the flow baffle and the pressure vessel wall, resulting in preliminary separation of oil on the wall of the pressure vessel while the separated oil is conveyed back into the compressor. Compressed air flows from beneath into the oil separator for air which is situated inside the cylinder formed by the flow baffle. The oil/air separator comprises one or more coalescing and/or drainage stages, e.g., a coalescing structure made of borosilicate glass fibers and a drainage structure made of polyester nonwoven fleece. The nonwoven fleece made of borosilicate glass fibers and the polyester nonwoven fleece are each applied to a supporting body made of metal. The flow passes through the oil/air separator from the outside to the inside. Small droplets of liquid are combined in the coalescing structure to form larger droplets, and some of them already settle out in the coalescing structure. Larger droplets leaving the coalescing structure fall further in the drainage structure and collect at the bottom of the oil/air separator. The oil at the bottom of the oil/air separator is conveyed back to the compressor device through a drainage line. The compressed air from which the oil has been removed is conveyed from the pressure vessel into a pressure storage vessel. The oil/air separator is mounted in the pressure vessel on an upper cover of the pressure vessel. The drainage line is passed through the upper cover or is connected to the upper cover. The separated oil is returned to the compressor device through a line from the passage through or connection to the upper cover.
One disadvantage of the system described here for separating oil from air, such as that used with screw compressors, is that connections for the drainage line and/or other lines for returning the oil to the compressor must be present on the upper cover. These lines are usually disconnected when changing the oil/air separator. There is the risk of damage to lines and/or gaskets. There is the possibility of leakage occurring during the assembly work. Changing the oil/air separator is made difficult.